Dual sound reproducing device



March 26, 1935. E. A. ROCKWELL DUAL SOUND REPRODUCING DEVICE Filed Dec. 26, 1951 2 Sheets- Sheet 2 mm NM INVENTOR Edward/4 K002 well ATTO R N EY Patented Mar. 26, 1935 UNITED STATES PATENT OFFICE Patent Engineering Corporation,

of Delaware a corporation Application December 26, 1931, Serial No. 583,251

12 Claims.

This invention relates to improvements in dual sound reproducing devices, such as are employed in loud speakers as used with talking motion pictures, radio receiving sets, etc. and has for its 5 principal object the production of a simple, efiicient and economic sound reproducing device employing two units, one of the usual electromagnetic or dynamic type and the other of the piezo electric, type.

Another object of the invention is to provide a device of this character embodying two units as aforesaid adapted for use in relatively small cabinets, the construction and arrangement of the units being such that diaphragm areas are obtained sufficiently large to faithfully reproduce sound waves in suiiicient volume.

A further object of the invention is to provide a device of this character wherein the faithful 20 secured with The invention consists substantially in the construction, combination, location and relative arrangement of parts as will be more fully hereinafter set forth as shown by the accompanying drawings and finally pointed out in the appended claims.

In many modern radio receiving sets or small outfits for talking motion pictures in the home, the sound reproducing device hereinafter termed a loud speaker is assembled with and mounted in the cabinet of the set. Heretofore the magnetic speaker has been used almost exclusively in commercial sets and in order to secure satisfactory and adequate sound reproduction it has been necessary to employ a diaphragm of from 40 6 to 12" in diameter. The diameter of the diaphragm of the averagecone speaker of the dynamic type is seldom less than 8" and when the diameter becomes 5" or less the reproduction and volume becomes unsatisfactory.

Radio receiving sets in which an electrically driven clock usually employing a synchronous motor are now coming into use. It is desirable that these sets shall not be larger than the ordinary mantel clock and should not be over 10" high, '7" wide and 6" deep. Obviously, the loud speaker in such a set cannot be of sufiicient diameter to secure satisfactory tone reproduction in sufficient volume. The present invention however permits of placing two speaker units in a 5 cabinet of the size mentioned and the area of the two diaphragms in the speaker units will be sufficient to produce in ample volume and faithful reproduction.

The invention will now be described employing a cabinet of approximately the dimensions herein given, utilizing as one of the speakers any suitable type of electromagnetic or dynamic device, many of which are well known, together with a piezo electric speaker, the driving element of which consists of a. Rochelle salt crystal as more fully described in the paper entitled The use of Rochelle salt crystals for electrical reproducers and microphones by C. Baldwin Sawyer, beginning on page 2020 of the Proceedings of the Institute of Radio Engineers for November, 1931, Vol. 19, No. 11.

In the accompanying drawings:

Figure 1 is a front view partly in section of the cabinet of a. radio receiving set containing two speaker units Figure 2 is a side view, partly in section, of the set, Figure 1;

Figure 3 is a isometric view of the two speaker units showing the magnetic unit partially surrounded and enclosed by the diaphragm of the crystal unit, and

Figure 4 is a diagram of the circuits of the two speaker units.

The cabinet or case 10 may be of any suitable construction and is provided with the usual opening 11 for the magnetic speaker and also openings on its sides, one of which is shown in the sectional half of Figure 1 at 12, these openings permitting the sound produced by the diaphragm 22 of the crystal speaker to find egress from the cabinet.

The magnetic speaker comprises the usual mounting frame 13 in which is supported the cone diaphragm 14 and on which is mounted the exciting coil 15. The usual voice coil 15' is attached to the diaphragm 14 in the usual manner. The speaker shown in the drawings is of the usual dynamic type and the step-down transformer 16 is mounted on the frame of the speaker as shown in Figure 2.

It will be understood that this magnetic speaker may be of any known type and is mounted in the cabinet in any suitable manner.

The cabinet is provided with a base plate 17, preferably of metal, on which is firmly secured at opposite ends by means of the clamps or lugs 0 18 the Rochelle salt crystal 19. The lugs 18 are in the lugs 20, 21 which are secured to the diaphragm 22 which is the full width of the cabinet and which extends around and over the magnetic unit enclosing the same on the sides as shown in Figure 2. In this construction the vibrations of the crystal impart vibrations tangentially to the plane of the diaphragm as more fully described in the patent to J. H. Van Wagenen No. 1,827,919 dated October 20, 1931 or the crystal may be mounted and operated as disclosed in the pending application, Serial No. 570,292 filed October 22, 1931.

In the space below the magnetic speaker and above the crystal 19 is positioned the chassis 23 containing the usual parts that are necessary to complete the radio receiver. The usual vacuum tubes are shown at 24, 25. The volume control is the projecting knob 26 and the tuning condenser knob is shown at 27. The usual dialv 28 is mounted immediately behind the tuning knob and may be seen through the aperture 29in the front of the cabinet.

The chassis complete may be pushed into the cabinet from the rear thereof, suitable flexible connections (not shown) being employed to 'connect the two speaker units in the circuit.

If desired, the two speaker units may be mounted upon and form part of the chassis so that all interior parts of the set including both speakers I suitable manner.

dynamic speaker magnet.

can be removed and replaced in the cabinet 10 without disconnecting any'wires, similar to the chassis shown and described in the application, Serial No. 570,292 aforesaid.

The two speaker units may be connected in any connect them in parallel as shown in Figure 4, the conductors 30, 31 being connected to the output of the radio receiving set and conductors 32; 33 to a suitable source of current for energizing the It will be observed that the capacity of the crystal 19 balances the impedance of the magnetic speaker and transformer 16. (In the event an ordinary magnetic speaker, not of the dynamic type, is used,-the transformer 16 may be om'tted and'the speaker winding connected directly across conductors 30, 31.) a

It is known that the impedance ofthe magnetic speaker increases with the frequency of the current impressed thereon and that the impedance of the crystal speaker decreases under the same conditions. Therefore, by properbalancing' of V the crystal capacity against the impedance of the magnetic speaker, that part of the output circuit containing the speakers can be given an average impedance value best adapted to the particular use to which the dual speaker is to be put.

It will be obvious from the foregoing specification and a study of the drawings that the combined area of the two speaker diaphragms 14 and 22 is much greater than could be obtained by any other arrangement in a cabinet of any given size and that several advantages are inherent in this arrangement. The fact that the sound is'emitted from the cabinet both from the front and sides is an advantage and it has been found that the quality of the reproduced music or speech is improved by reason of the diaphragm arrangement and by reason of the balancing of the impedance of the magnetic speaker by the capacity of the crystal speaker.

It has been found that by making the dynamic speaker responsive to lower tones and the crystal speaker responsive to higher tones that the combination results in the faithful reproduction of It has been found desirable to speech and music over a much greater range with greater fidelity than can be obtained by using either type of speaker separately. It appears that the dynamic speakers favor the base notes whereas the crystal speakers favor the treble or higher notes, so that this dual speaker is inherently perfect over a wide range of frequencies.

Although the invention has been disclosed in connection with the specific details of the preferred embodiment thereof, it must be understood that such details are not intended to be limitative of the invention except insofar as set forth in the accompanying claims.

' What is claimed is:

1; The combination of a magnetic speaker unit having a diaphragm and means for vibrating the diaphragm, a speaker un't having a diaphragm surrounding a portion of said magnetic speaker unit, means including a piezo electric crystal for vibrating said last diaphragm, and connections between said speaker units for simultaneously operating the same.

2. In combination with a magnetic speaker unit having a diaphragm I nd means for vibrating said diaphragm, a second speaker unit having a diaphragm partly embracing said first unit and including a piezo electric crystal means for operating said last diaphragm, a cabinet containing said speakers having separate apertures therein adjacent said diaphragms, and connections between said speaker units for simultaneously operating the same.

3. In combination, a magnetic speaker unit having a diaphragm and means for vibrating the diaphragm, a speaker unit having a diaphragm and piezo electric means for vibrating the diaphragm, a cabinet in which said units are mounted, said cabinet having a front wall and side walls, said magnetic unit having its diaphragm positioned adjacent said front of the cabinet and said crystal speaker having its diaphragm positioned adjacent said side wall thereof and embracing a portion of said magnetic unit, said cabinet having apertures in its walls adjacent said diaphragms, and connections between said speaker units for simultaneously operating the same.

4. In combination, a cabinet, loud speakers therein each speaker having separate means for driving the same, one of said speakers having a diaphragm flexed to form a portion of a cylinder, and radio receiving means in said cabinet connected to said speakers for simultaneously operating the same, said flexed diaphragm partly surrounding the radio receiving means and the other of said speakers.

5. In combination, a cabinet, a chassis containing radio receiving means in said cabinet, a loud speaker and a driver therefor in said cabinet, a second speaker in said cabinet having a diaphragm extending along the side of said chassis and partly embracing both the chassis and said first speaker, means below said chassis for operating said last diaphragm, and connections between said last speakers including said radio receiving means for simultaneously operating the same.

6. In combination, a cabinet, a loud speaker mounted therein, a chassis in said cabinet, a base plate in said cabinet, a second speaker comprising a diaphragm surrounding a portion of said chassis, actuating means for said diaphragm carried on said base plate, and connections between said speakers for simultaneously operating the same.

'7. In combination, a cabinet, a loud speaker unit including a cone diaphragm and actuating means therefor, said unit being secured to a wall of the cabinet, a second speaker unit having a flat diaphragm flexed to form a portion of a cylinder embracing said first speaker and actuating means therefor mounted subjacent said last diaphragm, and connections between said speakers for simultaneously actuating the same.

8. In combination, a loud speaker comprising a mounting frame, a diaphragm supported thereby, a voice coil secured to said diaphragm, an exciting coil secured to said frame, a second speaker having a diaphragm surrounding said exciting coil, said diaphragm extending over and around a portion of said frame and having its plane surface parallel with the axis thereof, a driver for said second speaker, and connections between said speakers for simultaneously operating the same.

9. In a radio receiving set, a cabinet, a loud speaker mounted therein with its diaphragm secured to the front thereof, a chassis in said cabinet, said chassis containing a volume control device and a tuning condenser, control knobs for said device and condenser, said knobs extending outwardly from the front of said cabinet, a second speaker within said cabinet having a diaphragm extending along the sides and across the top thereof, said speakers connected for operation to said chassis and adapted to be controlled by said knobs, and circuits including said speakers and connected to said volume control device and tuning condenser whereby said speakers may be simultaneously operated.

10. In a radio receiving set, a cabinet, a loud speaker therein, a base plate in said cabinet, a second speaker in said cabinet comprising diaphragm actuating means secured to said plate, a diaphragm connected to said means and extendsame.

11. In a radio receiving set, a cabinet, a loud speaker therein, a diaphragm extending along the inner side walls of the cabinet and across the top of same, means independent of said loud speaker for vibrating said diaphragm, and connections between said loud speaker and said vibrating means for simultaneously operating the same.

12. In a radio receiving set, a cabinet, a diaphragm within the cabinet covering substantially all the interior side and top wall thereof, means for vibrating said diaphragm supported by said cabinet, a loud speaker unit supported by said cabinet and having a portion of its operating parts within the space defined by said diaphragm, and connections to said means and said last speaker unit for actuating the same simultaneously.

EDWARD A. ROCKWELL. 

